A drilling fluid, sometimes known as a drilling mud, is a preparation of a base fluid (which may be oil-based or water-based), clays, and chemicals circulated in oil-well drilling for lubricating and cooling the bit, flushing the rock cuttings to the surface, and plastering the side of the well to prevent cave-ins. Drill-in fluids, sometimes known as reservoir drilling fluids, are a special category of drilling fluids used when drilling into and through the reservoir section of a subterranean formation. Generally, drill-in fluids include base fluids (such as brine), acid-soluble bridging agents, water-soluble polymers, pH stabilizers, and oxygen scavengers and exclude additives like clays and non-soluble weighting agents because such additives may plug pores and lead to difficult cleanup operations. Instead, heavy brines are generally used to set the density of the drill-in fluid, and water-soluble or water-swellable polymers are used as the rheology modifiers and fluid loss control agents. These polymers are generally biopolymers that degrade below 300° F., which reduces the viscosity of the fluid. At reservoir temperatures higher than 300° F., synthetic water-soluble polymers may be used, but such viscosifiers often cannot provide adequate viscosity at high temperatures, especially over the time frames for the drill-in operation. In addition, many viscosifiers are not as efficient when used in the brines used to provide the density of the drill-in fluid. Therefore, the thermal degradation of polymeric viscosifiers and the high salt content of the heavy brines continue to pose a very challenging hurdle for high temperature drill-in operations.